如何在没有GL_REPEAT的情况下将精灵包裹在立方体周围? [英] How do I wrap a sprite around a cube without GL_REPEAT?

问题描述

我正在使用OpenGL 3.2+.我创建了一个由8个顶点组成的多维数据集VBO(每个顶点包含8个浮点数:x，y，z，r，g，b，s，t)，一个EBO为该多维数据集创建面，以及一个VAO将其全部绑定在一起.

I'm using OpenGL 3.2+. I created a cube VBO of 8 verticies (each vertex consists of 8 floats: x,y,z,r,g,b,s,t), an EBO to create the faces for that cube, and a VAO to tie it all together.

我有一个由数百个16x16子画面组成的子画面图集.我正在尝试从该地图集中获得1个精灵，使其出现在立方体的所有侧面(任何方向都可以).

I have a sprite atlas consisting of hundreds of 16x16 sprites. I'm trying to get 1 sprite from that atlas to appear on all sides of the cube (any orientation is fine).

通过调整"s，t"参数，我可以使6张脸中的4张可以工作，但是我似乎无法让最后2张脸显示除随机垃圾之外的任何东西.

By tweaking the "s,t" parameters, I can get 4 of the 6 faces to work, but I can't seem to get the last 2 faces to show anything other than random garbage.

我需要修改我的着色器以在地图集上执行某种自定义UV包装吗?

Do I need to modify my shader to perform some kind of custom UV wrapping on the atlas?

推荐答案

通过调整"s，t"参数，我可以使6张脸中的4张可以工作，但是我似乎无法让最后2张脸显示除随机垃圾之外的任何东西.

By tweaking the "s,t" parameters, I can get 4 of the 6 faces to work, but I can't seem to get the last 2 faces to show anything other than random garbage.

至少必须对多维数据集的2条边使用单独的顶点和属性.这意味着您至少需要8 + 2 * 2 = 12个不同的顶点属性集.

At least you have to use separate vertices and attributes, for 2 edges of the cube. This means you need at least 8+2*2=12 different sets of vertex attributes.

         x  y  z    u  v
0  :    -1  1  1    0  0
1  :     1  1  1    1  0
2  :    -1 -1  1    0  1
3  :     1 -1  1    1  1
4  :    -1 -1 -1    0  0
5  :     1 -1 -1    1  0
6  :    -1  1 -1    0  1 
7  :     1  1 -1    1  1
8  :    -1  1  1    1  1
9  :    -1  1 -1    1  0
10 :     1  1  1    0  1
11 :     1  1 -1    0  0

请注意，索引属性为0、2、4和6的顶点属性集具有相同的u坐标0.索引属性为1、3、5和7的顶点属性集具有相同的u坐标.1.
如果要将纹理包装到四边形，则必须更改u和v坐标.因此，您必须添加单独的顶点属性集8、9、10和11.

Note, the vertex attribute sets with the indices 0, 2, 4 and 6 have an identically u-coordinate of 0. And the vertex attribute sets with the indices 1, 3, 5 and 7 have an identically u-coordinate of 1.
If you want to wrap a texture to a quad you have to vary the u and the v coordinates. Because of that you have to add the separated vertex attribute sets 8, 9, 10 and 11.

注意，如果要添加垂直于立方体侧面的法线向量，则需要24个顶点属性集.立方体的每一侧为4.

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